With the development of the optical and electronic technologies, liquid crystal displays (LCD) have been widely applied in electrical devices, such as televisions (TV), monitors, notebooks, personal digital assistant (PDA) and cell phones. Since an LCD is a non-self-light-emission plane display device, an external light source, such as a backlight source or a sidelight source, is thus necessary to the LCD. Accordingly, a backlight module with high luminance and uniformity becomes an essential light source of the LCD used to efficiently provide a high quality image.
FIG. 1 is an exploded view illustrating a traditional backlight module 200 of an LCD. The backlight module 200 includes a bezel 201, a frame 204, a light source 212, a reflecting sheet 216, a light guide plate 214 and a plurality of optical films 210, by which the light emitting from the light source 212 and then reacting with the light guide plate 214 and the reflecting sheet 216 can be transformed into a plane light source. The frame 204 which is disposed in the bezel 201 and has a main part 204a and a containing space 205. The light source 212 is disposed in the containing space 205. The reflecting sheet 216, the light guide plate 214 and the optical films 210 are sequentially stacked in the containing space 205. Each of the optical films 210 has at least one protrusion portion 210a, and the main part 204a of the frame 204 has at least one notch 204b or through-hole 204c corresponding to the protrusion portion 210a of the optical films 210, whereby the optical films 210 can be easily assembled on the frame 204 in accordance with the position of the notch 204b or the through-hole 204c. 
FIG. 2 illustrates the detailed structure of the main part 204a of the frame 204 having the notch 204b formed thereon. FIG. 3 is a cross sectional view of the frame 204 depicted along the cutting line A-A′ shown in the FIG. 2; and FIG. 4 is a cross sectional view of the frame 204 depicted along the cutting line B-B′ shown in the FIG. 2. For the purpose of clearly description, FIGS. 3 and 4 further illustrate elements other than the frame 204, such as the bezel 201, the light guide plate 214, the reflecting sheet 216, the optical films 210 and a panel 219 of an LCD in order to distinguish the correlations among those elements. Referring to FIG. 3, because the emitting light of the light source 212 (not shown) passing through the light guide plate 214 may be blocked by the frame 204, thus the light may hardly leak there from. However, undesired light leakage may occur at other points. Referring to FIG. 4, because there exists a notch 204b or a through-hole 204c formed on the frame 204, thus the light emitting form the light guide plate 214 may leak out of the bezel 201 without any obstruction, so as to result in a severe lateral light leakage problem.
Traditionally, a viewing angle inspection may be carried out before an LCD is delivered, in order to keep the LCD having a horizontal viewing angle ranging around 20 degree and a vertical viewing angle ranging around 40 degree. Currently, in order to satisfy the customer requirement, an LCD with a wide viewing angle is provided, wherein the viewing angle is enlarged to 85 degree. However, as the viewing angle is enlarged, the problems of light leakage may get worse and worse, especially at the position on which the notch 204b or a through-hole 204c is formed (shown in the FIG. 4). Therefore, how to prevent light of an LCD with a wide viewing angle leaking from the notch or the through-hole is still a challenge to the art.